1. Field of the Invention
The present invention relates to computed tomography imaging systems and techniques, and more particularly to novel computed tomography and tomosynthesis systems and methods.
2. Background
Projection x-ray imaging is a widely performed diagnostic imaging procedure for producing two dimensional images. Such images are commonly acquired using computed radiography (“CR”) or direct digital radiography (“DR”) systems. Projection x-ray imaging, however, suffers from the fundamental limitation that three-dimensional anatomic structures are superimposed in the two-dimensional projection image such that overlying structures often obscure the visibility of an underlying structure of interest.
X-ray computed tomography (“CT”) was developed, at least in part, to enable the visualization of adjacent anatomic structures in cross-sectional slices through a patient. In conventional geometric CT, the x-ray tube and imaging detector are spaced apart on opposite sides of the patient. The x-ray tube and detector are synchronously moved completely (or near completely) around the patient during the x-ray exposure so the detectors (film, plates, or other detectors) follow and capture the exposures. Conventional CT produces a plane of images in focus at the focal plane of motion and all other locations within the image both above and below the focal plane are generally out of focus and thus blurred and less visible in the resulting image. X-ray CT techniques are known for high patient dose, long exposure and image acquisition times and high procedure cost.
Tomosynthesis is a more recent improvement over conventional projection x-ray imaging, particularly for certain applications. Similar to conventional CT, tomosynthesis combines x-ray exposure and capture and processing with the x-ray/detector techniques generally used in more recent conventional CT. Thus, the x-ray source and x-ray detector arc similarly located on opposite sides of the patient and the x-ray the and detector also move synchronously and continuously about a fulcrum residing in the plane of interest. In contrast to conventional CT, however, the movement around the patient using tomosynthesis is generally much more limited. Tomosynthesis typically uses a small rotation angle of the x-ray head and a smaller number of x-ray exposures to obtain a limited set of data. This limited data is then digitally processed to yield the desired images. Advantages of tomosynthesis over CT include reduced imaging and acquisition time and reduced radiation exposure.
Tomosynthesis allows the digital reconstruction of a generally arbitrary number of cross-sectional tomographic slices through an object from a limited number of acquired projection x-ray images to produce a three-dimensional perspective. The position and thickness of the tomographic slices can be varied in order to achieve better visualization overlapping anatomic structures or to control other aspects of the diagnosis.
Current CT and tomosynthesis systems, however, remain limited in application. For example, conventional tomosynthesis equipment and techniques require the patient to remain still during the exposure process. Remaining still during the exposure and detection period can be challenging for many patients. In mammography techniques a positioning mechanism is used to secure the breast stationary during the exposure process. While the technique allows for detailed imaging, patients often complain of pain and discomfort resulting from the positioning mechanism. What is needed is a tomography and tomosynthesis device capable of making the necessary x-ray exposure quickly so as to shorten the time necessary for the patient to remain still or be secured by a positioning mechanism.
Another disadvantage of currently available CT and computed tomosynthesis systems is their limited availability due to, among other reasons, high initial and operating costs as well as the need for highly trained operators. CT and tomosynthesis systems may not be as readily available in areas lacking the resources to fund such systems. Thus, what is also needed is CT and tomosynthesis systems that are simpler, less complex and less expensive to manufacture and operate. In this way, advanced imaging can provided at more reasonably pricing so as to be made available to less affluent medical centers as well as reducing operating and maintenance costs.